This invention relates to welding devices and particularly to capacitor discharge bolt or stud welding apparatuses.
Such apparatuses include a welding generator set, a welding gun, and at least two flexible current-carrying cables for establishing a movable electrical connection between the welding set and the welding gun, and between the welding set and the base metal onto which an element is to be welded by the welding gun.
As a rule, a capacitor bank in the welding set stores the electrical energy required for the welding operation. A current supply in the welding set recharges the capacitor from the line. A welding current switch starts the weld. If necessary, the apparatus also includes controls or regulating devices which usually form part of the set for adjusting the particular welding variables such as the voltage, welding time, the capacitance of the capacitor bank, and the like. The system may also include safety devices. In the welding gun, suitable means hold the element, such as a welding bolt or stud, etc., to be welded. A trigger or release switch in the gun permits closing of the welding current switch so as to actuate the welding operation.
Such capacitor-discharge welding operations generally involve a welding element having a forwardly extending tip, that is a thin projecting point, which serves to strike the arc. Thus, once the tip on the element makes contact with the base metal to which the element is to be welded, and the welding operation is initiated, the capacitor bank in the welding set discharges rapidly with a relatively steep current rise. This causes instantaneous melting and evaporation of the tip. An arc between the element and the base metal follows. The arc forms a weld pool in the base metal over the entire welding area. The gun then plunges the element into the weld pool. This plunging movement may be initiated before the welding switch is closed or at some time thereafter. When the available welding energy stored in the capacitor bank is discharged the weld pool cools and the stud or bolt remains welded in the weld metal. The actual welding time, that is the striking of the arc and the plunging of the welding element into the weld pool, lasts about 1 to 3 milliseconds.
In such systems the welding set is heavier and more unwieldy than the welding gun. Therefore, for assembly work using welding operations, the welding set is first installed at a convenient site. Then, the welding gun is connected with the welding set by means of flexible welding current cables and, if necessary, control cables. In this way it is possible to perform welding operations at scattered sites spaced at given distances from one another. An operator simply moves the welding gun along without having to move the welding set for each operation.
Hitherto, the flexible welding-current cables have taken the form of two individual lines independent of one another. It allows one of the cables to serve as a grounding connection for the base material onto which the elements are to be affixed by welding. Specifically, it allows the grounding connection to remain established at a given point on the base material as the welding gun is moved repeatedly in order to perform the individual welding operations. Moreover, lines having conductive crosssections as large as those required in the case of welding-current cables for stud welding machines are usually supplied by cable manufacturers as individual lines. Such individual lines permit maximum freedom of movement with the welding gun. This practice also follows the usual arc welding procedure which uses individual lines.
While such capacitor discharge welding apparatuses are suitable for many purposes, they produce welds which vary undesirably when used in assembly procedures where a gun is moved from one position to another.
Suggestions have been made for overcoming this problem by issuing special instructions to the operators for compensating for shifts in positions or by having the operators interconnect compensating circuits for different positions.
Such instructions are often not followed so that the problem of non-uniform welds remains. Automatic compensating devices would be cumbersome and costly.
An object of the present invention is to improve welding devices.
Another object of the invention is to overcome these problems.